It's unrelated: there's no combo box in use in the installer... Tcl/Tk can throw different errors that look alike, especially since it gives a full backtrace (with common calls corresponding to the main loop at the bottom of the stack).
In my experience open source 3D drivers are extremely poor, performance-wise, when compared to the proprietary drivers, which I would therefore recommend you to use, unless they got serious bugs, which happens with ATI (got a Mobility Radeon 9600/9700 that crashes every time the mouse pointer shape changes while the CPU is 100% loaded... a hardware bug that ATI never worked around in their driver while Open Source drivers got it right...). Also, another valid reason for using Open Source drivers with ATI is the fact that their abyssal support of legacy products makes it impossible to get a working driver for modern kernels or Xorg servers only a few years after you bought their graphics card...
My advice: never buy ATI. Get the only serious and working stuff: get a NVIDIA card !